Semiconductor



Patented Oct. 12, 1948 UNITED STATES PATENT OFFICE 2,450,887 samconnue'roa Charles Alexander Escoflery, East Orange, N. J.,

assignor to Federal Telephone and Radio Corporation, New York, N. Y., a corporation of Delaware No Drawing. Application November 20, 1944.

Serial No. 584,409

The present invention relates to semi-conductors and particularly to high voltage selenium conducting surface to the supply electrode. This transition resistance must be as low as possible and must be independent of voltage if the operation of the rectifier is to be satisfactory. The characteristic resistance curve of the blocking layer itself is dependent upon its chemical and physical composition and the magnitude of the resistances in both direction of current flow is primarily determined by the conductivity of the selenium itself.

It has been recognized before that the conductivity of selenium can be materially increased by a thorough conversion into a crystalline term by annealing it at a temperature close to the melting point and that the conductivity of selenium can be further increased by the addition of materials, such as pulverized halogen salts of heavy metals, alkalies, carbon powder, or organic compounds. After conversion the additional materials either appear as undecomposed matters having certain conductivity embodied in the selenium or they are mainly decomposed into oxides or selenides of good conductivity. These latter are conductive bodies and form dangerous shunting paths in the selenium and in the blocking layer itself.

In view of these unfavorable results it was suggested to add to selenium such material which avoids impurities in the selenium layer. Realizing realm. (Cl.17536.6)

plum-bromide brought about an increase in the forward-conductivity of the blocking layer, but at the same time a proportionate increase in the back-conductivity had to be accepted.

Although the latter proposal appeared to be another step in the advancement of the art, it did not provide satisfaction in those cases in which it was essential to increase the forward-conductivity of the rectifier without increasing at the same time the reverse-conductivity.

In the co-pending application of Escoilery 8i- Merva, Serial No. 564,408, flied November 20, 1944, assigned to the. same assignee as the present application, it is suggested to add such material to the selenium which not only avoids the introduction of impurities into the selenium, and also avoid the formation of compounds of selenium with the'metallic impurities, but at the same time increases the forward-conductivity of the rectifier withoutchanging its reverse-conductivity, that means a decrease in the relation of forwardresistance to back-resistance, and allows also a higher voltage than achieved before. This is achieved by adding one substance of the group 1C], IBr, IC1a,IBrs. It is there further suggested the advantage of adding pure halogens to pure selenium, it was tried to add halogens in its pure form to the selenium- However, difficulties were encountered to achieve a thorough mixture of the halogens and the selenium and as a further step in the advancement of the art and in the desire v to avoid the forming of dangerous shunting paths in the selenium, it has been suggested to admix selenium-chloride or selenium-bromide to the seto provide one substance of the mentioned group in relation of 100 weight parts of selenium'to from .001 up to .5 weight part of the mentioned substance.

It is the object of the present invention to provide a mixture of a plurality of substances of the group oi ICl, IBr, I01: and 113m to the selenium. It is a further object of the present invention to provide a plurality of substances of the above mentioned group in relation of 100 weight parts oi selenium to from .001 up to .5 weight part of all the mentioned admixed substances together.-

It is still another object of the present invention to provide a method of producing a semi-conductor for selenium rectiflers which comprises admixing selenium with a plurality of substances from the group of 1C], IBr, 1C]; and IBra in the mentioned relation.

For the achievement of the best possible conductivity and the highest increase of the forwardconductivity of the semi-conducting layer an admixture of the mentioned substances of .005 to .1

to selenium has been proven of particular beneficial' advantage. 7

It has been also found that the admixture according to the present invention, that means the addition of more than one halogen compound to the selenium, in contradiction to the above mentioned application in which only one halogen compound is added to the selenium, shows beneficial results where it is not only important to increase the forward-conductivity without increasing the reverse-conductivity but also to use a disc, designed for a certain voltage, at a still higher voltage than is allowed to use in the disc according to the above mentioned application.

The novel construction of the present rectifier has the advantage of using less rectifying discs within the rectifier stack for a certain predetermined forward-conductivity where until now a greater number of rectifying discs had to be used.

There are diiierent ways available to provide a thorough mixture of the halogen compounds with the selenium. One'way is to pulverlze the halogen compounds and mix them with the selenium powder. another is to put the halogen compounds as 101 into a crucible, which compounds are covered thereafter with selenium, using the capacity of the mentioned compounds to harden at a temperature slightly below ordinary room temperature and to change into fumes by heating up the crucible, thereby streaming through the selenium positioned above them and mixing thoroughly with them. Still another way of adding substances of thementioned group of halogen compounds is to dissolve the substances in an alcohol such as methyl, ethyl, etc., which alcohol will escape upon heating and the mentioned substances will remain in the selenium.

4|. While I have disclosed the principles of my invention in connection with several different embodiments. it will be understood that these embodiments are given by way of example only and not as limiting the scope of the invention as set forth in the objects and the appended claim.

What I claim is:

In a process for manufacturing selenium rectiiier elements the improvement that comprises incorporating in the selenium layer a minor proportion of a plurality of substances selected from the class consisting of iodine compounds of chicrine and iodine compounds of bromine.

CHARLES ALEXANDER. ESCOFFERY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,173,249 Boer et al. Sept. 19, 1939 2,226,715 Geisler Dec. 81, 1940 2,227,827 Dubar Jan. 7, 1941 2,316,995 Waibel Apr; 20, 1943 FOREIGN PATENTS Number Country Date 472,951 Great Britain Sept. 30, 1937 

